1. Field of the Invention
This invention involves the calculated performance improvements expected from a particularly new class of compounds, geminal-bis(difluoramino)-substituted heterocyclic nitramines, when formulated into explosives and propellants. Further, this invention involves 5,5-bis(difluoramino)hexahydropyrimidine derivatives, related geminal-bis(difluoramino)alkylene derivatives, and novel precursors to these new derivatives, by the use of certain key intermediates which allow formation of this target structural subcomponent.
2. Description of the Related Art
The calculated performance improvements expected from geminal-bis(difluoramino)-substituted heterocyclic nitramines when formulated into explosives and propellants has been reported. [Miller, Materials Research Society Proceedings 1996, 418, 3] One example of a highly desirable structure, described by Miller, is a derivative of 5,5-bis(difluoramino)hexahydro-1,3-dinitropyrimidine which has the following formula: 
wherein R2 is selected from the group consisting of hydrogen, alkyl, and substituted alkyl. The highly desirable structure, given the acronym RNFX by Miller, exists when R2 is hydrogen.
Methodology for preparing a geminal-bis(difluoramino)-substituted nitrogenous heterocycle has been reported by Chapman et al. [Journal of Organic Chemistry 1998, 63, 1566], who describe the preparation of 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-bis(4-nitrobenzenesulfonyl)-1,5-diazocine; this intermediate has been converted to the corresponding nitramine, 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-dinitro-1,5-diazocine, given the acronym HNFX [Chapman et al, Journal of Organic Chemistry, 1999, 64, 960]. However the preparation of cyclic derivatives of 2,2-bis(difluoramino)-N,Nxe2x80x2-dinitro-1,3-propanediamine in which the nitramine components are linked with a single-carbon bridge, such as RNFX, has not been previously described.
This invention involves novel and nonintuitive methods for the preparation of certain derivatives of 2,2-bis(difluoramino)-N-nitro-1,3-propanediamine which are suitable precursors leading to RNFX. However,the synthesis of certain examples of this class of compounds is difficult and nonintuitive. The certain examples that are particularly synthetically difficult are molecules that incorporate the geminal-bis(difluoramino)alkylene [C(NF2)2] component and the nitramine component [Nxe2x80x94NO2] in close proximity, especially when separated by only a methylene (CH2) link in order to maintain a low fuel-to-oxidizer component ratio and concomitantly high oxygen balance in the product molecule. The invention also involves novel and nonintuitive methods for the preparation of RNFX, a specific member of a general class of compounds with the substructure 2,2-bis(difluoramino)-N-nitro-1,3-propanediamine. RNFX is produced by the use of key intermediates which allow formation of the target structural subcomponents, 2,2-bis(difluoramino)-N-nitro-1,3-propanediamine and a more specific substructure of 2,2-bis(difluoramino)-N,Nxe2x80x2-dinitro-1,3-propanediamine, which has the following structure: 
Also, this invention comprises certain unprecedented nitramides and nitramines suitable for conversion to RNFX and a variety of other difluoramino-substituted heterocyclic nitramines. An important aspect of the present invention is the substitution on heterocyclic precursors"" nitrogen atoms and intermediate nitramides"" nitrogen atoms. The nitrogen atoms of heterocyclic precursors (such as pyrimidines) must be suitably substituted, or xe2x80x9cprotected,xe2x80x9d during the process of difluoramination to allow this process to proceed to geminal-bis(difluoramino)alkylene derivatives. Without suitable protection of proximate multiple nitrogens, especially those separated from reacting carbonyl sites by a short bridge, such as methylene, the process of difluoramination of ketone intermediates does not proceed to geminal-bis(difluoramino)alkylene derivatives. The result is mono(difluoramino)alkylene derivatives or no reaction at all.
An object of this invention is to create a novel explosive and propellant involving geminal-bis(difluoramino)-substituted heterocyclic nitramines.
Another object of this invention is to create a novel method of producing 5,5-bis(difluoramino)hexahydro-1,3-dinitropyrimidine using electronegatively substituted pyrimidines and other novel intermediates leading to RNFX.